An experimental electricity-free cooling system is under development at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. The device is still just a concept in its early stages, but it’s a promising solution for remote communities in sunny regions which lack infrastructure.
A shocking 940 million people (13% of the global population) don’t have access to electricity, and most of them live in blistering hot, arid countries like Mali or Niger.
Buildings get very hot without electricity to at least plug in a fan. Fortunately, KAUST’s invention only needs saltwater and sunlight to produce a cooling effect. It utilizes a natural “phase-change” phenomenon in which salt crystals absorb heat energy as they dissolve within the water. As a result, warm water rapidly cools if salt is added (as the salt dissolves). It’s a basic chemical reaction.
Furthermore, average global temperatures are rising because of climate change. Unfortunately, the electricity needed to power fans and air conditioners to keep cool generates carbon emissions, which cause climate change. It’s a vicious cycle that keeps global temperatures continuously rising.
Fans and AC account for 10% of the world’s electricity consumption, according to a 2018 International Energy Agency report. Therefore, KAUST’s new technology is also a promising solution to reducing electricity consumption related to keeping cool, which could lower the grid’s carbon footprint.
The researchers experimented with various salts, landing on ammonium nitrate as the best choice because it dissolves quickly and it’s a common fertilizer; thus, it’s affordable, and sourcing it should be simple for commercial and personal applications. Ammonium nitrate’s high water solubility results in a cooling power that is four times greater than ammonium chloride – the next-best salt.
Another great aspect of the technology is how the salt can be reused repeatedly. The technology constitutes two parts to take advantage of this. One part holds the water as the salt dissolves. Then, the subject that water to solar energy, which causes the liquid to heat and evaporate, leaving behind the salt solids. The water could also be reused by including a solar still in the system.
The entire process is slow, taking half an hour to restore the salt in a liter of water. However, the technology can store solar energy for later use, allowing cooling to be available on-demand, not only when the salts are regenerated.
Dr. Peng Wang, an engineering and environmental science professor at KAUST leading the research, explained:
You can use today’s solar energy to provide cooling power in a week.
The researchers tested the proof-of-concept prototype in the laboratory, finding the temperature remained below 50ºF (10ºC) for 8 hours and under 59ºF (15ºC) for over 15 hours.
In the experiments, they added ammonium nitrate into the water in a metal cup and put it inside a sealed polystyrene foam box. The temperature of the cup dropped as the salt dissolved, bringing the water from room temperature (about 77ºF/25ºC) to 38ºF (3.6ºC) within about 20 minutes. From there, it stayed below 50ºF for 8 hours and 59ºF for over 15 hours.
The results demonstrate how the system could also be used to refrigerate food or to keep medicine cool. Dr. Wang said:
In underdeveloped regions, this can help them store food for a couple more days.
The team now wants to build a full-scale demonstration unit since they’ve proven the concept works on a laboratory scale. Dr. Wang said:
It can be as big as a regular fridge or as small as your lunchbox size. It could also come as a waterbed. If you replace the water inside your mattress, you have yourself a cooling mattress. As for the regenerating system itself, that can be kept on the roof or in the backyard.
While the technology isn’t powerful enough to keep an entire home cool, it could be used in conjunction with conventional electricity to minimize demand on the grid or in the countryside, where connecting a home to the grid isn’t cost-effective. However, it’s ideal for smaller tasks like food storage and medicine preservation.
Wang said:
Our system is used at a small scale, and your expectation should not be high, but it’s passive, driven by renewable energy, it has a very small carbon footprint, and it gives you flexibility.
The only downfall is sourcing water in regions where water scarcity is a problem. Although, one solution for such a situation could be to use an atmospheric water generator (AWG) that sucks water out of the air. Zero Mass Water makes an AWG called a hydro-panel that uses sunlight to power the technology – no electricity required.
The company has helped many families living with water scarcity problems in the Navajo Nation with its water-harvesting solar panels. Zero Mass Water’s hydro panels could also generate the water needed for KAUST’s cooling system!
